A variety of diseases exist which require regular treatment by injection of a medicament. Such injection can be performed by either medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses once or several times per day. It is known to couple a supplemental device to an insulin injection device for recording information about the doses that are administered. Supplemental devices may be used to record information about the various times at which insulin doses are administered and the quantity of insulin administered during each such dose.
One previously proposed insulin injection device, specifically the Solostar™ injection pen sold by Sanofi, is provided with a window in its outer surface. A sleeve inside the Solostar™ injection pen (known as the number sleeve) is caused to rotate when an amount of insulin is dialled or dispensed. Numbers on the number sleeve successively align with the window as the sleeve rotates. When an amount of insulin has been dialled, the number corresponding to the dialled amount of insulin (in International Units) is displayed in the window. When insulin is dispensed, rotation of the number sleeve causes the number displayed in the window to be that associated with the dialled amount of insulin remaining in the pen yet to be dispensed.
It has been proposed for a supplemental device to gather information on how much insulin is delivered from a Solostar™ injection pen by analysing information displayed in the above mentioned window. In particular WO2011/117212 describes a supplemental device provided with optical character recognition (OCR) functionality for reading numbers aligned with the window of an injection device to determine quantities of insulin dialled or delivered.
Problems arise however when the number sleeve is caused to rotate above a certain speed. When this occurs numbers displayed in the window appear blurry to the supplemental device, thereby hindering the supplemental device from gathering information concerning the quantity of insulin dialled or dispensed.